This invention relates to an improvement in molten bath gasifier-melters for producing molten iron with continuous melting of iron feed in a bath. The invented method is particularly applicable to the use of non-metallurgical coals.
It is known to feed pulverized coal and oxygen to the bottom of a melter-gasifier and to inject oxygen to burn some of the coal gas evolved from the molten bath in order to heat and melt the iron charge fed to the top of the vessel. Difficulties encountered are inefficient heating of the bath and localized combustion.
U.S. Pat. No. 4,317,677 of Weber, et al., teaches a fluidized bed gasifier wherein a fluidized bed of coal is formed above a hearth. Water or steam and/or hydrocarbon are introduced through the side of the gasifier and oxygen is also introduced through the side of the gasifier at a lower elevation. The fluidized bed gasifier is coupled directly to a direct reduction furnace above the gasifier, the gases from the gasifier being removed, cleaned, cooled, then introduced into the furnace wherein they act as reducing gases. The direct reduced iron drops directly from the discharge of the furnace through the fluidized bed into the molten metal bath. This differs substantially from the present invention wherein gas from the gasifier-melter is mixed with some recycled gas and introduced to a shaft furnace and the spent top gas is cleaned and cooled, then a portion is mixed with the gasifier gas and a second portion is introduced directly into the gasifier-melter. The present invention makes more efficient use of the gases than any previously known molten bath gasifier-melter.
Other prior art patents relating to molten bath gasifier-melters, including Hartwig U.S. Pat. No. 4,007,034, Morvay U.S. Pat. No. 2,750,278, Sanzenbacher, U.S. Pat. No. 4,238,226, and Halley U.S. Pat. No. 2,889,219, do not use a fluidized bed.
Another known process utilizes coal gas from a molten bath coal gasifier-melter to produce direct reduced iron. In this process it is undesirable to produce excess gas which requires export for usage outside of the battery limits of an associated direct reduction plant or the utility system which serves the direct reduction plant. The gas produced is employed to produce a highly metallized direct reduced iron. Direct reduction plants generally produce products having about 92% metallization.